Endoscope observation system

ABSTRACT

An endoscope observation system for in vivo cellular observation is disclosed that includes an illumination optical system having a light source for supplying illumination light to an object, an objective optical system that forms a magnified image of the object such that the absolute value of the image scale factor exceeds unity, and an image pickup unit that detects the magnified image. The illumination optical system is provided with a wavelength selection means for dividing, among the blue, green, and red wavelength ranges in the illumination light from the light source, either the blue wavelength range or the red wavelength range into two wavelength bands T 1  and T 2 , with the wavelength band T 1  being nearer the green wavelength range than is the wavelength band T 2 , and light in the wavelength band T 1  is prevented from illuminating the object. An in vivo cellular observation method is also disclosed using an endoscope.

This application claims the benefit of foreign priority from JapanesePatent Application No. 2003-094028, filed Mar. 31, 2003, the contents ofwhich are hereby incorporated by reference. This is a divisionalapplication of allowed U.S. application Ser. No. 10/808,309 that wasfiled Mar. 25, 2004.

BACKGROUND OF THE INVENTION

Conventional endoscopes have a large field of view that is in the rangeof about 90° to 140° so that tissues inside a body can be observedwithout overlooking lesions. They also change the distance to the objectin order to obtain either magnified or reduced-sized images of an objectto be observed, and thus have a large depth of field for a fixed focuspoint so that objects at distances between 3 mm and 50 mm can beobserved without refocusing.

Conventional endoscopes also have an image scale factor with an absolutevalue of about 30 to 50 when the image is displayed on a monitor havinga 14-inch screen, which is sufficient to observe diseased tissues. Zoomoptical systems are used in order to obtain further magnified images,with the absolute value of the image scale factor being approximately 70when displayed on a monitor having a 14-inch screen. The zoom opticalsystem typically has a built-in, zoom lens driving mechanism. As aresult, the endoscope has an insert tip with an outer diameter that islarger than 10 mm and requires complex operations. Such endoscopes havelimited applications.

The manner in which living tissues are observed using a conventionalendoscope will now be described with reference to FIG. 1. Living tissuesto be observed by a conventional endoscope often include a mucousmembrane 1, transparent epithelial cells 2 and underlying parenchymaltissues 3 in which blood vessels run. Light illumination emitted at theendoscope tip part 4 must first pass through the mucous membrane and thetransparent epithelial cells before reaching the parenchymal tissues.The illumination light which reaches the parenchymal tissues 3 isscattered by the parenchymal tissues 3. Of the light that is scatteredby the parenchymal tissues, most re-enters the epithelial cells. Theillumination light is also scattered by cell walls 5 and cell nuclei 6when it is transmitted through the transparent epithelial cells. Thelight rays B1, B2 that are scattered by the cell nuclei of theepithelial cells are weak and thus the light rays that are scattered bythe parenchymal tissues dominate. Consequently, in a conventionalendoscope, only the parenchymal tissues are observed through anobjective optical system.

When it becomes difficult to provide a diagnosis of an abnormality byobserving images of a tissue, such as when a lesion is very small, asuspicious-looking tissue may be excised during the course of anendoscopic examination. The cells of the excised tissue are thenexamined under a microscope. Whereas an endoscope generally usesincident illumination from an illumination optical system that ispositioned around an objective optical system, a microscope insteadgenerally uses an objective optical system and an illumination opticalsystem that are positioned on opposite sides of a sample. The sample isnormally pre-processed in order to make it more suitable forobservation, such as by removing the parenchymal tissues by slicing thesample thin in order to reduce scattering and/or by staining the samplein order provide better contrast.

The manner in which a sample is observed using a microscope will now bedescribed with reference to FIG. 2. A prepared sample is fixed onto acover glass 7 and illuminated from below with light from an illuminationsystem 8. Illumination light rays A1′, A2′ are diffracted by the cellwalls and cell nuclei as they transmit through the sample 9. Thediffracted light rays B1′, B2′ interfere with one another bothconstructively and destructively, producing interference fringes thatprovide visible contrast. Thus, one can observe the sample by using anobjective optical system 10 placed above the sample.

Laser-scanning-type confocal endoscopes which have a resolutionsufficient for cellular observation have been proposed that may beinserted within a living body. These typically use a confocal opticalsystem having a pinhole for passing an Airy disk light pattern at aposition that is conjugate to the image plane, and the confocal opticalsystem thus acquires diffraction-limited information for each point ofan object in the field of view. A laser beam directed from a lightemitting optical system scans the object, and information obtained fromthe reflected light from the object for each point is combined so as toproduce an image representing either a two-dimensional or athree-dimensional object. High resolution can thus be realized not onlywithin the image plane, but also in the depth direction.

It takes from several days to several weeks to identify abnormal tissueusing conventional procedures wherein living tissues are excised andexamined in vitro. Moreover, a cellular sample that is isolated andfixed for observation is only a tiny part of a removed tissue. Thus,although a cellular sample provides information on cellular structures,it is incapable of providing important functional information, such asinformation concerning fluid circulation within cells. This is becausethe circumstances between in vitro and in vivo examination arecompletely different. Thus, there is a need for magnifying endoscopesthat will provide real-time, in vivo observation of intact living cells.

In order to form cellular images of a lesion within a living body, asmall-sized image pickup unit is necessary that is provided with anobjective optical system with an image scale factor having an absolutevalue that is nearly as high as that of a microscope and which provideshigh resolution. The objective optical system used in a conventionalendoscope does not meet these requirements. As mentioned previously, ina conventional endoscope as shown in FIG. 1, the illumination light isdiffracted by the cell walls and cell nuclei as it transmits through theepithelial cells. The diffracted light rays B1, B2 are weak and thelight rays A1, A2 that are scattered by the parenchymal tissues aredominant. Consequently, using a convention endoscope, only data from theparenchymal tissues is imaged by the objective optical system.

Although a conventional objective optical system as used in microscopesis satisfactory as far as providing sufficient imaging performance, suchan objective optical system is too large for easy insertion into aliving body. Laser-scanning-type confocal endoscopes have a problem inthat their scanning speeds are still too slow for real-time, in vivoobservations. Thus, as described above, an image pickup unit that meetsthe requirements for in vivo cellular observation has not yet beenrealized.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to a magnifying image pickup unit suitablefor in vivo cellular observation, an endoscope for in vivo cellularobservation, and an in vivo cellular observation method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings, whichare given by way of illustration only and thus are not limitative of thepresent invention, wherein:

FIG. 1 is an illustration to explain a principle of living tissueobservation using a prior art endoscope;

FIG. 2 is an illustration to explain a principle of excised sampleobservation using a microscope;

FIG. 3 shows a configuration of a magnifying image pickup unit accordingto the present invention, along with other components for displayingendoscopic images;

FIG. 4 shows the spectral wavelength distribution of an image detectedby an image pickup unit according to the present invention;

FIG. 5 shows a magnified image of cells that have been stained forobservation according to an embodiment of the present invention;

FIG. 6 shows the appearance of cells in the background that overlapcells of interest in the foreground;

FIG. 7 shows the spectral transmittance of a wavelength selection filterused in an embodiment of the present invention;

FIG. 8 shows an image in which information from regions other thanregions at a desired depth is eliminated;

FIG. 9 shows the spectral transmittance of another wavelength selectionfilter used in an embodiment of the present invention;

FIGS. 10(a) and 10(b) are a side cross section and an end view,respectively, of an insert tip part of an endoscope imaging system thatuses specific wavelengths for observation;

FIGS. 11(a) and 11(b) are a cross-sectional view and an end view,respectively, of the magnifying image pickup unit of Embodiment 1;

FIGS. 12(a) and 12(b) are a cross-sectional view and an end view,respectively, of the magnifying image pickup unit of Embodiment 2;

FIG. 13 illustrates an illumination method suitable for in vivo cellularobservation;

FIG. 14 is a flow chart of the steps for in vivo cellular observationaccording to the present invention; and

FIG. 15 shows an image pickup unit that simultaneously displays bothconventional endoscope images and fluorescent images for observation ofcell nuclei.

DETAILED DESCRIPTION

A magnifying image pickup unit according to the present invention thatis applied to an endoscope for use in in vivo cellular observation willnow be described.

First, a conventional endoscope having a wide-angle field of view isused so as to provide a thorough examination of tissues in an area ofthe body without overlooking any area that may contain diseased tissue.Because it is difficult to diagnose a region of tissue using imagesobserved with a conventional endoscope, an endoscope to which themagnifying image pickup unit of the present invention is applied(hereinafter termed a magnifying endoscope) is used to cellularlyexamine a region of tissue.

For magnified cellular observation, coloring agents generally will havebeen previously delivered to the area, if necessary. Within a certaintime period after the coloring agent is delivered, the difference in thetime required for the cell nuclei, the cell walls, and the other cellcomponents to excrete the coloring agent creates contrast in the object.Then, a magnifying endoscope is guided to the region and contact is madewith the object at the tip of the magnifying endoscope whileobservations using a conventional endoscope are continued. Preferably, atissue image from a conventional endoscope and a cellular image from amagnifying endoscope are displayed simultaneously on a TV monitor. Inthis way, the magnifying endoscope can be guided precisely to a verysmall, targeted region within an extensive observation field of view inorder to magnify and observe cell nuclei and cell walls.

Before providing a detailed explanation of a magnifying image pickupunit according to the present invention, the requirements for an imagepickup unit that may be used in a magnifying endoscope will bediscussed. First, the scale factor required for visualizing finecellular structures will be discussed. The overall observation scalefactor bm of an image observed on a display monitor is given by thefollowing equation:bm=|βo|·bd  Equation (A)where

βo is the image scale factor of the objective optical system, namely,the height of the image as formed on the image pickup element divided bythe actual height of the object, and

bd is the display scale factor, defined as the monitor display screenelement size divided by the image pickup element size.

Conventional endoscopes realize an overall observation scale factor ofabout 30 to 50 when the images are viewed on a 14-inch display monitor.Zoom optical systems having a magnifying function realize an image scalefactor with an absolute value of approximately 70. However, an overallobservation scale factor in the range of approximately 200 to 2000 isnecessary for cellular observation when viewed on a 14-inch monitor.Therefore, it is desired that the objective optical system satisfies thefollowing conditions:1<|βo|≦10  Condition (1)0.9≦|cos wy′/cos wy|≦1.1  Condition (2)where

βo is the image scale factor of the objective optical system,

wy′ is the incident angle at which a chief ray corresponding to thelargest field angle enters the image pickup surface, and

wy is the half-field angle.

When the lower limit of Condition (2) is not satisfied, the incidentangles of rays onto the image pickup element will be too large, failingto maintain uniform image qualities (for example, color reproducibilityand brightness) within the field of view. When the upper limit ofCondition (2) is not satisfied, the field angle will be too large,failing to ensure a required scale factor.

Image resolution will now be discussed. Diseased tissues can beidentified with an image resolution in the range of millimeters andsub-millimeters. However, cellular observations require an imageresolution in the range of microns and sub-microns. In order to formdetailed images of an object that is both transparent and provides onlya small difference in refractive indexes, the interference of diffractedlight rays from the object may be used so as to provide images havingenhanced contrast. The objective optical system needs to have a largernumerical aperture NA on the object side so as to collect higher ordersof diffracted light rays and, preferably, satisfies the followingCondition (3):0.1≦NA≦0.8  Condition (3)

In the case where the cell walls are observed, it is preferable tosatisfy the following Condition (3′):0.3≦NA≦0.8  Condition (3′)

In addition, in order to obtain both high contrast and high resolutionimaging, the objective optical system should have a resolution higherthan that determined by the pitch of the image pickup element, withoutexceeding the resolution determined by the diffraction limit. Theobjective optical system preferably satisfies the following Condition(4):0.1≦|p·NA ²/(0.61·λ·βo)≦0.8  Condition (4)where

p is the pixel size of the image pickup element,

NA is the numerical aperture of the objective optical system on theobject side;

λ is the e-line wavelength (i.e., λ=0.546 μm), and

βo is the image scale factor of the objective optical system.

When the lower limit of Condition (4) is not satisfied, sufficientcontrast will not be obtained. When the upper limit of Condition (4) isnot satisfied, aberrations become difficult to correct, resulting in thefailure to obtain fine images.

Miniaturization (i.e., down-sizing) of the magnifying endoscope will nowbe discussed. It is desirable that the magnifying endoscope have anouter diameter Φ of less than 4 mm in order that it may be guided to anobservation object through a treatment tool insert channel of aconventional endoscope. Accordingly, it is desirable that the objectiveoptical system be miniaturized so as to have an outer diameter Φ of lessthan 2 mm.

A desired, small-sized, objective optical system having an image scalefactor with a large absolute value and a high resolution comprises, inorder from the object side: a lens unit having positive refractive powerand an aperture stop, wherein the following Condition (5) is satisfied:0.2≦Φ1/(Φ2·f1)≦2  Condition (5)where

Φ1 is the diameter of the aperture stop,

Φ2 is the largest outer diameter of the objective optical system, and

f1 is the focal length of the lens unit having a positive refractivepower.

Condition (5) prevents the objective optical system from having a largerdiameter in association with a larger numerical aperture NA, thusfacilitating miniaturization. When the lower limit of Condition (5) isnot satisfied, the objective optical system will have a larger totallength and a larger maximum diameter, hampering miniaturization. Whenthe upper limit of Condition (5) is not satisfied, aberrations becomedifficult to correct.

In order to obtain a flat image surface, it is desirable that theobjective optical system be formed of, in order from the object side, afront lens unit having positive refractive power, an aperture stop, anda rear lens unit having positive refractive power. In such a case, thefollowing Condition (6) is preferably satisfied in order to achieve bothminiaturization and an image scale factor having a large absolute value:2≦f2/f1≦10  Condition (6)where

f1 is the focal length of the front lens unit, and

f2 is the focal length of the rear lens unit.

When the lower limit of Condition (6) is not satisfied, a required imagescale factor having a large absolute value will not be maintained. Whenthe upper limit of Condition (6) is not satisfied, a larger overalllength and a larger maximum diameter of the objective optical systemwill hamper miniaturization.

Various embodiments of a magnifying image pickup unit of the presentinvention will now be described.

EMBODIMENT 1

The structure of Embodiment 1 of the magnifying image pickup unit willnow be discussed with reference to FIGS. 11(a) and 11(b), which show aside cross section and an end view, respectively, of the magnifyingimage pickup unit according to this embodiment.

The objective unit comprises an objective lens unit 101 having a uniformdiameter in an objective frame 102. The objective lens unit 101 consistsof, in order from the object side: a first lens group G1 having positiverefractive power, an aperture stop 103, and a second lens group G2having positive refractive power. An image pickup element 105 is affixedto an image pickup frame 106 via a cover glass 104, thereby forming animage sensor unit.

The image pickup unit is focused by changing the distance 107 betweenthe objective lens unit and the image sensor unit. An insert section fora magnifying endoscope is constructed of a hard tip member 108 and anouter sheath member 110. The image pickup unit is affixed to the insertsection via an intermediate member 109.

FIG. 11(b) is an end view looking in the direction indicated by thearrow A in FIG. 11(a). The intermediate member 109 has cutouts(indicated by cross-hatching) at its periphery through which anillumination fiber 111 may be inserted and affixed thereto. After theintermediate member 109 and illumination fiber are affixed to the hardtip member 108, the image pickup unit is inserted and affixed to theintermediate member 109.

Referring to FIG. 11(a), when adjustment is required, for example, inthe absolute value of the image scale factor, the gaps 112 a and 112 bthat are provided before and after the aperture stop 103 can be adjustedto provide a larger or smaller space, if necessary. To do so, gapadjustment rings that are made of ultra-thin plates may be used for gapadjustment. A gap adjustment part is designed to hold a stack of suchultra-thin plates. A different number of ultra-thin plates may be usedaccording to the varied gap sizes needed as a result of an assemblyprocess in which parts having a variety of dimensional errors are used.

Table 1 below lists the surface number #, in order from the object side,the radius of curvature R (in mm) of each surface, the on-axis surfacespacing D (in mm), as well as the refractive index Nd and the Abbenumber νd (both at the d-line) of each optical element of Embodiment 1.Also listed is the outer lens diameter LD of each lens element ofEmbodiment 1. In the bottom portion of the Table are listed the distanceto the object and the image height, in mm. TABLE 1 # R D Nd υd LD 1 ∞0.46 1.5183 64.14 1 2 0.84 0.17 3 ∞ 0.4 1.7323 54.68 1 4 −0.817 0.05 51.353 0.65 1.7323 54.68 1 6 −0.703 0.25 1.7044 30.131 7 −3.804 0.09 8 ∞(stop) 0.03 9 ∞ 0.4 1.5156 75.00 1 10 ∞ 0.2 11 1.566 0.4 1.67 48.32 1 12−1.566 0.2 13 −0.729 0.3 1.5198 52.43 1 14 ∞ 0.56 15 ∞ 0.4 1.5183 64.1416 ∞ 0.01 1.5119 63.00 17 ∞ 0.4 1.6138 50.20 18 ∞ 0.01 1.5220 63.00 19 ∞0Distance to the object = 0Image height = 0.500

EMBODIMENT 2

FIG. 12(a) is a side cross section of the magnifying image pickup unitof Embodiment 2, and FIG. 12(b) shows an end view looking in thedirection of the arrow A shown in FIG. 12(a).

Table 2 below lists the surface number #, in order from the object side,the radius of curvature R (in mm) of each surface, the on-axis surfacespacing D (in mm), as well as the refractive index Nd, and the Abbenumber νd (both at the d-line) of each optical element for Embodiment 2.Also listed is the outer lens diameter LD of each lens element ofEmbodiment 2. In the bottom portion of the Table are listed the distanceto the object and the image height, in mm. TABLE 2 # R D Nd υd LD 1 ∞0.88 1.8882 40.76 1.2 2 −0.703 0.05 3 ∞ 0.4 1.5183 64.14 1.2 4 −1.4850.05 5 2.085 0.76 1.8081 46.57 1.2 6 −0.703 0.25 1.8126 25.42 1.2 7 ∞0.05 8 ∞ (stop) 0.03 9 ∞ 0.4 1.5156 75.00 1.2 10 ∞ 0.43 11 1.131 0.51.8395 42.72 1.2 12 −3.127 0.2 13 −1.061 0.3 1.8126 25.42 1.2 14 ∞ 0.215 −0.592 0.3 1.8081 46.57 1.2 16 2.132 0.77 1.8126 25.42 1.2 17 −1.2620.77 18 ∞ 0.4 1.5183 64.14 19 ∞ 0.01 1.5119 63.00 20 ∞ 0.4 1.6138 50.2021 ∞ 0.01 1.5220 63.00 22 ∞ 0Distance to the object = 0Image height = 0.500

Table 3 below lists the values of the variables of interest forEmbodiments 1 and 2. TABLE 3 Embodiment Embodiment item legend unit 1 2image scale factor βo −2.678847 −6.63 focal length of front f1 [mm]0.765 0.591 lens group focal length of rear f2 [mm] 3.476 4.557 lensgroup focal length f [mm] 0.657 0.797 half of field angle wy [deg] 6.1413.95 exit angle of chief ray wy′ [deg] 13.965 6.02 numerical aperture NA0.2184 0.55 on the object side stop diameter Φ1 [mm] 0.36 0.66 largestlens diameter Φ2 [mm] 1 1.2 pitch P [μm] 4 4 reference wavelength λ [μm]0.546 0.546

Table 4 below lists the Conditions (1)-(6) and the values correspondingthereto for Embodiments 1 and 2. TABLE 4 Condition Embodiment EmbodimentNo. Condition 1 2 1 1 < |βo| ≦ 10 2.680 6.630 2 0.9 ≦ |cos wy′/cos wy| ≦1.1 0.976 0.997 3 0.1 ≦ NA ≦ 0.8 0.220 0.550 4 0.1 ≦ |p · NA²/ 0.2150.544 (0.61 · λ · βo)| ≦ 0.8 5 0.2 ≦ Φ1/(Φ2 · f1) ≦ 2 0.471 0.931 6 2 ≦f2/f1 ≦ 10 4.544 7.711

A video observation system suitable for in vivo cellular observationwill now be described. As mentioned above, living tissues of interestoften include parenchymal tissues with transparent epithelial cellsoverlying the parenchymal tissues. The following techniques are used inorder to create sufficient contrast between the cell nuclei and othercell portions so as to enable observation of the epithelial cells withina targeted observation region with no interference from the underlyingparenchymal tissues. For example, a video observation system suitablefor distinctly observing a layer of cells that have been stained bluefor improved contrast has the following configuration.

FIG. 3 shows a configuration for the video observation system that usesthe magnifying image pickup unit of the present invention. Theillumination light supplied by a light source device 11 illuminates anobject 12 via a magnifying image pickup unit 13. The light source device11 is provided with a wavelength selection filter 14, which ispositioned in the illumination light path, as required, to produceillumination light having a wavelength profile suitable for cellularobservation. When illumination light having a visible wavelength rangeis used to illuminate living tissue, the shorter wavelengths thatcorrespond to blue reach only the surface of the living tissue. Thesewavelengths are useful to obtain information specific to the epithelialcells of the living tissue. Light having wavelengths around 500 nm(corresponding to the color green) reaches only slightly below thesurface of living tissue. On the other hand, light wavelengthscorresponding to the color red reach relatively deep inside livingtissue.

An image is formed by the objective optical system of the magnifyingimage pickup unit 13 at the image pickup surface of the image pickupelement. The image pickup unit converts the image into electricalsignals and sends them to an image processing unit 15. In processingimage data of the visible region, green wavelength components are usedto produce the brightness information of the object. In this way, imagesare obtained that are similar to those acquired through the human eye.The image data that are processed by the image processing unit 15 aredisplayed on a TV monitor 16.

When the cells that have been stained blue are illuminated by whitelight that equally contains blue, green, and red components, theportions that have been stained blue appear blue while unstainedportions appear white. FIG. 4 shows a wavelength profile of a cellularimage formed by the magnifying image pickup unit, with the Y-axis (theordinate) being the light intensity in arbitrary units and the X-axis(the abscissa) being the wavelength in nm. Unstained portions do notabsorb specific light wavelengths and thus provide a nearly flatwavelength profile, as is shown by the solid lines 17. Portions thathave been stained blue absorb red light and give a wavelength profilewith a drop in intensity primarily for the red component, as shown bythe broken lines 18.

In this way, the contrast between the background (the unstainedportions, shown by the solid lines) and the cell nuclei and walls (thestained portions, shown by the broken lines) appears as a difference inlight reflection 19 that is due to light absorption that occursprimarily at the longer wavelengths (i.e., the red component) for imagesobtained using the magnifying image pickup unit.

As shown in FIG. 1, the epithelial cells are vertically layered. Whenobserving the cells in a specific layer, the images of layers of cellsthat are not at the depth of interest in the epithelial cells and thecells of the underlying parenchymal tissues overlap in the background,thereby reducing the image contrast. Cell walls are only slightlystained by the staining processes as compared to cell nuclei. FIG. 6illustrates the situation where the images of cells that are not ofinterest overlap in the background, and the cell walls are barelyrecognizable.

In order to eliminate unwanted images (i.e., noise) overlapping in thebackground, the light that transmits information about the parenchymaltissues, and the cell layers that are not at the depth of interest canbe cut off in the illumination light path or in the objective opticalsystem before the light is detected by the image pickup element. In thisembodiment of the video observation system, a filter for cutting off aspecific range of wavelengths is inserted in the illumination light pathin order to eliminate unnecessary wavelength components from theillumination light. In this case, unnecessary components are mainly thelonger wavelengths of the visible light range, such as red light.However, it is not desirable to eliminate all the red light componentsbecause this cuts off the wavelength components that serve to providecontrast between the portions that have been stained blue and theunstained portions.

The present invention uses, for the wavelength selection filter 14 ofthe light source, a filter having a spectral transmittance as shown inFIG. 7. FIG. 7 shows the spectral transmittance by solid line with theordinate (i.e, the Y-axis) being the transmittance and the abscissa(i.e., the X-axis) being the wavelength in nm. More specifically, amongthe illumination light that includes the blue, green, and red wavelengthranges, the illumination light of the red wavelength range is dividedinto two wavelength bands R1 and R2. Among the wavelength bands R1 andR2, the wavelength band R1 that is nearer the green wavelength range iscut off by the filter and thus prevented from illuminating the object.The wavelength band R1 may be, for example, the range 600 nm<λ<700 nm,and the wavelength band R2 may be, for example, the range 700 nm<λ<800nm. FIG. 8 shows an image in which information from regions other thanregions at a desired depth is eliminated.

Using illumination light with the wavelength band R1 cut off allowslimited light to reach the parenchymal tissues and the cell layers thatare not at the depth of interest, but are within the depth of field ofthe objective optical system. Thus, the image resolution in the depthdirection is improved by preventing overlapping of unwanted images. Onthe other hand, the light in the wavelength band R2 contributes toproducing contrast between the cell nuclei that have been stained blueverses the cell walls and other cell portions that remain relativelyunstained. Thus, a clear image of the cell layer of interest is obtainedwith the information from unnecessary depths being eliminated. Thetransmittance characteristic shown in FIG. 7 can be realized using adichroic filter.

A contrast medium can be used to enhance only the cell nuclei. In such acase, the contrast medium that is absorbed by the cell nuclei has outerelectrons that are excited by excitation light and which emitfluorescent light when they return to the ground state. This fluorescentlight can be observed in order to accurately identify the cell nuclei.In particular, the video observation system according to the presentinvention is useful for a method where a gene contrast medium, such as agene marker (for example GFP) that reacts with light, can be injectedinto the cells and the identification of a specific gene that occurswhen healthy cells are transformed into diseased cells such as cancermay be accomplished.

In the method above, the gene in a living cell is altered immediatelybefore the onset of disease and a gene marker, which takes no actionamong the normal cells, identifies diseased areas and emits weakfluorescence in response to excitation light. Thus, the videoobservation system used for this observation is desirably provided witha hypersensitive camera.

It is preferable that the video observation system for fluorescent imageobservation of cell nuclei be used in combination with a conventionalendoscope. FIG. 15 shows an example of such a combination. Thefluorescent image observation system is formed as a thin endoscope thathas an elongated portion 41. A magnifying image pickup unit 42 of thefluorescent image observation system is mounted on the distal end of theelongated portion. The reference numeral 43 denotes a conventionalendoscope that has a channel 44 that extends from the distal end to theproximal end (not shown) of the conventional endoscope. The conventionalendoscope also has an observation window 45 as well as illuminationwindows 46 and 47 at its distal end. The channel is also used forinserting treatment tools. The elongated portion 41 of the fluorescentimage observation system is inserted into the channel 44 from theproximal end of the conventional endoscope 43 and comes out of thechannel 44 via the opening in the channel. The endoscope observationsystem is inserted into a body cavity to be observed. The conventionalendoscope provides images of the elongated portion 41 that protrudesfrom the channel for guiding the magnifying image pickup unit 42 to thetargeted observation region. The TV monitor 16 (shown in FIG. 3)displays images from the conventional endoscope as well as fluorescentimages from the image pickup unit simultaneously, thereby providing moreprecise and accurate observations.

When a contrast medium that primarily absorbs light of wavelengthsshorter than 480 nm and emits fluorescent light having wavelengthslonger than 470 nm is used, a preferred wavelength selection filter 14for the light source has a spectral transmittance as shown in FIG. 9. InFIG. 9, the spectral transmittance is shown by the solid lines with theordinate illustrating the transmittance and the abscissa being thewavelength in nm.

More specifically, the illumination light of the blue wavelength rangeis divided into two wavelength bands B1 and B2 and, among the wavelengthbands B1 and B2, the wavelength band B1 that is nearer the greenwavelength range is cut off by the filter. For example, the wavelengthband B1 may lie in the range 450 nm<x<500 nm and the wavelength band B2may lie in the range 350 nm<x<450 nm. In such a case, the objectiveoptical system may be provided with a filter that transmits light havingwavelengths longer than about 470 nm and cuts off light havingwavelengths shorter than about 470 nm. Thus, fluorescent images can beobserved while the excitation light is cut off. The light of thewavelength band B1 that includes the excitation and fluorescentwavelengths is cut off from the illumination light. This enables clearimages using weak fluorescence to be observed with no interference fromthe excitation light.

The wavelength selection filter 14 for the light source device can beused with a filter that reduces the light intensity of either the greenor red wavelength range. This prevents unnecessary image noise in thebackground of fluorescent images of the cell nuclei and allows aconventional endoscope to produce conventional observation images ofliving tissue.

An illumination method suitable for in vivo cellular observation isdescribed hereafter with reference to FIG. 13. The tip of anillumination unit 30 that serves to illuminate an object and the tip ofan objective optical system 31 that serves to form images on the imagepickup surface of an image pickup element using light from the objectare located at the tip 32 of an endoscope. The central axis L of theillumination field of the illumination unit 30 is substantially parallelto and shifted from the central axis F of the field of view of theobjective optical system 31 by a distance d; thus, the center line ofthe illumination field and the center line of the objective opticalsystem (i.e., of the observation field) are directed in substantiallythe same direction. The endoscope tip 32 is placed adjacent livingtissue in order to observe the living tissue. The distance between atargeted region of the living tissue and the endoscope tip is adjustedso that the targeted region among the epithelial cells and parenchymaltissues which form the living tissue is “in-focus” (i.e., centrallylocated within the depth of field of the objective optical system). Asshown in FIG. 13, the distance between the position of the epithelialcells 34 and endoscope tip 32 is X1 and the distance between theposition of the parenchymal tissues 33 and the endoscope tip 32 is X2.

The conventional endoscope uses the field of view F2 of the objectiveoptical system to observe the parenchymal tissues at the distance of X2.The distance d between the central axis L of the illumination field andthe central axis F of the field of view at the endoscope tip isdetermined in a manner such that the illumination field L2, which ispositioned in front of the endoscope tip by a distance X2, includes thefield of view F2 in order to ensure a uniform brightness in the field ofview F2. The distance X2 is several millimeters to several tens ofmillimeters.

On the other hand, the magnifying endoscope uses an objective opticalsystem having a field of view F1 in order to observe the epithelialcells at a distance X1. The distance X1 is within the range of zero toseveral microns, that is, substantially zero. Therefore, as shown inFIG. 13, the illumination field L1 a, which is positioned in front ofthe endoscope tip by the distance X1, may fail to include the field ofview F1 of the magnifying endoscope even when the distance d between thecentral axes of the illumination field L and the field of view F at theendoscope tip is reduced. Consequently, it is understood that theconventional illumination method fails to ensure a uniform brightness inthe field of view F1 of the objective optical system. The presentinvention provides an illumination method in which the parenchymaltissues that are positioned still farther in front of the endoscope tipthan the farthest position of the depth of field of the objectiveoptical system are utilized for uniformly illuminating the field of viewF1 of the objective optical system.

As shown in FIG. 13, an observation target is at a distance X1 from theendoscope tip 32 and the parenchymal tissues 33 are at a distance of X2from the endoscope tip. The illumination light emitted from theendoscope tip 32 reaches the parenchymal tissues via the illuminationfield L1 a. The parenchymal tissues 33 serve as reflecting andscattering surfaces and thus scatter the illumination light. It isassumed that the illumination light emitted from the endoscope tip 32has a Gaussian light distribution profile, and the effective lightdistribution angle of illumination will herein be defined as a lightdistribution angle ω that provides a light intensity that is 1/e timesthe light intensity on-axis, where e is the base of the naturallogarithm.

As shown in FIG. 13, the illumination light emitted from the endoscopetip 32 is transmitted through the living tissues at the lightdistribution angle ω1′ before it reaches the parenchymal tissues 33.After being reflected and scattered by the parenchymal tissues, theillumination light is emitted at the light distribution angle ω2′ andthereafter it reaches the epithelial cells at the in-focus region 34 andforms the illumination field L1 b at a distance X1 from the endoscopetip that includes the field of view F1 of the objective optical system.Consequently, uniform brightness is ensured in the field of view F1 ofthe objective optical system. Thus, an object placed in contact with adistal end of the observation unit so that a light source that does notdirectly illuminate an observation field of view illuminates an area oftissue outside the observation field of view, and the illuminated tissuescatters light from the light source so as to illuminate the observationfield of view. The observation unit is then used to observe an image ofthe observation field with a scale factor larger than 1.

The light distribution angles ω1′ and ω2′ are light distribution angleswithin living tissues. The following Equations (B) and (C) are used toconvert these light distribution angles to the equivalent lightdistribution angles ω1, ω2 in air.sin ω1=1.33·sin ω1′  Equation (B)sin ω2=1.33·sin ω2′  Equation (C)

The parenchymal tissues are outside the depth of field of the objectiveoptical system, therefore, the light reflected and scattered by theparenchymal tissues is not imaged and thus merely the illuminationeffect on the epithelial cells is obtained. It is preferred that thedistance d at the endoscope tip between the central axes of theillumination field L and the field of view F satisfies the followingCondition (7):1≦log(d/(X1·tan ω))≦3  Condition (7)where

d is the distance between the central axis of the illumination field andthe central axis of the field of view of the objective optical system,

X1 is the distance between the leading surface of the endoscope (i.e.,the endoscope tip) and the in-focus point of the objective opticalsystem, and

ω is the light distribution angle that provides a light intensity thatis 1/e times the light intensity on-axis, where e is the base of thenatural logarithm.

When the upper limit of Condition (7) is not satisfied, uniformbrightness will not be ensured in the field of view of the objectiveoptical system. When the lower limit of Condition (7) is not satisfied,it will be difficult to locate the tips of the illumination unit and theobjective optical system at the endoscope tip with the outer diameter ofthe endoscope tip being maintained small.

In addition, the following Condition (8) is preferably satisfied:5≦d/(X2·tan ω)≦30  Condition (8)where

d and ω are as defined above, and

X2 is the distance between the leading surface of the endoscope (i.e.,the endoscope tip) and the reflecting and scattering surfaces, such asthe parenchymal tissues.

When the upper and lower limits of Condition (8) are not satisfied,uniform brightness will not be ensured in the field of view of theobjective optical system.

It is also preferred that the following Condition (9) be satisfied:0.5≦log(X2/X1)  Condition (9)where

X2 and X1 are as defined above.

When Condition (9) is not satisfied, the parenchymal tissues are imagedin the field of view, deteriorating the image quality.

Table 5 below lists various values of X2, X1, d and ω pertaining toEmbodiments 1 and 2 of the present invention. TABLE 5 EmbodimentEmbodiment item legend unit 1 2 scatterer distance X2 [mm] 0.1 0.1objective in-focus distance X1 [mm] 0.015 0.002 illumination parallax d[mm] 0.8 1 illumination distribution ω [deg] 35 35 angle

Table 6 below lists the Conditions (7)-(9) and the value of each forEmbodiments 1 and 2. TABLE 6 Condition Embodiment Embodiment No.Condition 1 2 7 1 ≦ log(d/(X1 · tan ω)) ≦ 3 1.88 2.85 8 5 ≦ d/(X2 · tanω) ≦ 30 11.4 14.3 9 0.5 ≦ log (X2/X1) 0.82 1.7

The method for diagnosing the presence/absence of abnormal cells (i.e.,whether cells are cancerous or not) from magnified cell images will nowbe described.

FIG. 5 shows stained cells that are magnified and observed according toEmbodiment 1. The image pickup unit used in the magnifying endoscopeobservation system is set for a scale factor that allows several tens toseveral hundreds of nuclei to be observed on a monitor. For example,several tens to several hundreds of cell nuclei are displayed on amonitor and the cell density in the observation field of view can beevaluated based on the distance between cell nuclei in order to diagnosethe presence/absence of abnormal cells. The cell density can be comparedwith normal samples and statistically analyzed.

The magnifying endoscope observation system above is specified for aresolution and a magnification sufficient for nucleic observation. Withthe observation scale factor further increased, the image pickup unitdisplays several cell nuclei on a monitor and the number of cell nucleiin a unit area is translated to the cell size, or the cell nuclei areevaluated for shape, in order to diagnose the presence/absence ofabnormal cells. For example, cancerous cells present particularcharacteristics such as increased size and irregular shapes. Thus, thesize and shape of cell nuclei can be evaluated in order to diagnosecancerous cells.

FIG. 8 shows cell nuclei and cell walls that are magnified and observedaccording to Embodiment 2 of the present invention. The magnifyingendoscope observation system is set for a scale factor that allowsseveral nuclei to be observed on a monitor. The ratio of the area S′ ofthe cell nuclei divided by the area S within the cell walls in the fieldof view is herein defined as the “occupancy” of the nuclei in the cells,and is used to diagnose the presence/absence of abnormal cells. For thisanalysis, the magnifying endoscope observation system is specified so asto have a resolution and contrast sufficient for observation of bothcell nuclei and cell walls.

FIG. 14 is a flow chart of a series of procedures for the in vivocellular observation described above. As noted in the drawing, there isa pre-treatment stage, followed by a cell visualization stage, followedby a stage of abnormal cell diagnosis. During pre-treatment, thefollowing steps are performed: detect a suspicious region by using aconventional endoscope; deliver a coloring agent using a conventionalendoscope; selectively stain cell parts due to differences in time forcells to intake or excrete the coloring agent; and guide a magnifyingendoscope to the suspicious region and contact the tip thereof to theregion for observation. During cell visualization the following step isperformed: emit illumination light having selected wavelengths; theillumination light including wavelength band T2, with the wavelengthband T1 being nearer the green wavelength range than is the wavelengthband T2, for visualizing cells due to differences in absorbency, andwavelength band T1 for cutting off data at depths not targeted. Duringabnormal cell diagnosis, the following steps are performed: displayseveral tens to several hundreds of cell nuclei; and, display severalcell nuclei and the cell walls. Note that in CELL VISUALIZATION of FIG.14, the second and third boxes are not separate steps; instead, theseboxes merely indicate the details of the selected wavelengths.

The system described above in which specific wavelength bands are usedfrom a white light source provides excellent flexibility where pluralwavelength properties are selectively used in the illumination light,depending on the observation target and the selected coloring agent. Onthe other hand, where the wavelength property of the illumination lightis predetermined, a single color illumination light, for example, can beused to further simplify the configuration.

An endoscope tip part of an endoscope imaging system specified forobservation with specific wavelengths of light is illustrated in FIGS.10(a) and 10(b), with FIG. 10(a) being a side cross section and FIG.10(b) being an end view. The image pickup unit according to the presentinvention has a small observation distance and therefore, the lightsource can be formed of LEDs 20 that emit a single color at low power.The LEDs 20 can be mounted in the endoscope body. Furthermore, when LEDsare installed at the tip of the endoscope, a light transmission opticalfiber can be eliminated. Because aberration correction is necessary foronly a single color when an LED light source is used, the fluorescentimage observation system 21 can be provided with a simplified opticalsystem that includes, for example, a single aspherical lens 23positioned in front of a stop 24, and an image pickup element 25positioned after the stop 24 at the image surface. Alternatively, pluralspherical lenses (not shown) can be used in lieu of using a singleaspherical lens.

An image pickup element that has been made compact and simplified asdescribed above provides more freedom in mounting such an image pickupunit on a medical device such as an endoscope. For example, an imagepickup unit may be combined with a treatment tool such as a catheter orlaser probe that uses a flexible, insertable device. Or, an image pickupunit may be combined with a non-flexible treatment tool by making theimage pickup unit compact and with a shape such as a pen or capsule byusing wireless transmission of image data.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention. Rather, the scopeof the invention shall be defined as set forth in the following claimsand their legal equivalents. All such modifications as would be obviousto one skilled in the art are intended to be included within the scopeof the following claims.

1-13. (canceled)
 14. An endoscope observation system comprising: animage pickup unit that includes a magnifying objective optical systemhaving an image scale factor with an absolute value that is greater thanunity; and a light source for supplying illumination light, the lightsource being an LED that emits single color light rays directly onto anobject to be observed by the endoscope.
 15. The endoscope observationsystem according to claim 14, and further comprising: an elongatedportion adapted for insertion into a channel installed in anotherendoscope; wherein the image pickup unit is mounted at a distal end ofthe elongated portion.
 16. (canceled)